Method and system for measuring energy expenditure and foot incline in individuals

ABSTRACT

A method and system for measuring energy expenditure of individuals by measuring force from a plurality of foot-borne force sensitive resistors and calculating incline from a foot-borne tri-axial accelerometer.

PRIORITY CLAIM

Priority is claimed to U.S. Provisional Patent Application Ser. No.61/070,413, filed Mar. 20, 2008, which is hereby incorporated herein byreference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates generally to activity monitoring, footinclination, and estimation of energy expenditure of an individual.

2. Related Art

An inactive lifestyle is often seen in our children, especiallybeginning in 9-14 year-olds. Behavior patterns often begin in thisage-group and track into adulthood. Lack of physical activity affectsearly onset diabetes, obesity, heart disease, and other chronicillnesses. These illnesses have a negative effect on a child'squality-of-life and functional status, and increase parent burden.

Physical inactivity is an important, modifiable lifestyle factor that isan essential factor in energy balance, and thus key in obesityprevention and treatment. Physical inactivity also contributes to riskfor increased morbidity and mortality of other chronic conditions, andis an independent risk factor for cardiovascular disease, the leadingcause of death in the United States. There is a well-documented trend ofincreasing sedentary activity for all ages in the United States andrecommendations for increasing physical activity. What is known aboutchildren's physical activity is that: (a) physical activity begins todecline in the 9-14 year age group, especially for girls, (b) patternsof activity tend to track from childhood into adulthood; and (c)inactivity is related to increased risk for morbidity of chronicconditions. However, recommendations for assessment, health promotion,and intervention are difficult to implement and evaluate, challenged bythe lack of adequate screening and measurement tools that arecost-effective, efficient, easily usable, reliable and valid.Appropriate, reliable and valid screening and measurement tools arecritical if clinicians and researchers working with children are tofully understand activity or lack thereof, and if we are to fullyexplicate the component of activity/inactivity as a contributing factorin obesity and other conditions in children.

Self-report physical activity provides adequate and reliable data, butvalidity data vary widely and are inconsistent. Motion monitors areconsidered more objective, less burdensome, and less invasive than othermeasurement techniques. However, current motion monitors involve highmonetary expense and use burden. Additionally, current devices aredifficult to stabilize on the waistband, especially for large-waistedchildren whose girth adversely effects placement and diminishesmeasurement accuracy. Furthermore, activity on an incline, forcedistribution under the foot, and inverted activities (i.e. playgroundactivities) have not been able to be efficiently measured.

SUMMARY OF THE INVENTION

The inventors of the present invention have recognized that it wouldadvantageous to develop a method and system for measuring energyexpenditure of individuals, such as children with inactive behaviorpatterns that affect early onset diabetes, obesity, heart disease andother chronic illnesses, by measuring force from a plurality offoot-borne force sensitive resistors and calculating incline from afoot-borne tri-axial accelerometer. In addition, the inventors of thepresent invention have recognized that it would be advantageous todevelop a method and device for integrating cost effective, efficient,and less burdensome measurement tools that help to better understandchildren's physical activity, provide a more substantial foundation forintervention and monitoring, and improve overall clinical utility.Additionally, the inventors of the present invention have recognizedthat it would be advantageous to develop a method and device having aninnovative and inexpensive, motion tracker developed to maximizeavailable technology in motion-monitored physical activity measurement.

The invention provides a method for analyzing motion of an individual.At least a tri-axial accelerometer is affixed with respect to a user'sfoot. Accelerometer data is collected from the tri-axial accelerometer.Incline during stance phase is determined based on the accelerometerdata from the tri-axial accelerometer using an electronic processor.

In accordance with one aspect of the present invention, energyexpenditure of the individual can be determined based on theaccelerometer data using the electronic processor.

In accordance with another aspect of the present invention, stance phasecan be determined by using force sensitive resistors. A plurality offorce sensitive resistors can be affixed with respect to the user'sfoot. Force data from the plurality of force sensitive resistors iscollected. Stance phase is determined based on the force data from theplurality of force sensitive resistors using the electronic processor.

In accordance with another aspect of the present invention, stance phasecan be determined by using the tri-axial accelerometer.

The invention also provides a method for measuring activity in anindividual. Data is collected from a multi-sensor insole disposed in ashoe, including force data from a plurality of force sensitive resistorsand accelerometer data from a tri-axial accelerometer. The data from thesensors of the multi-sensor insole is determined with an electronicprocessor to determine the energy expenditure of the individual based onthe force data and inclination of the shoe with respect to the groundduring stance phase over a period of time. In accordance with one aspectof the present invention, different types of activities can beidentified using pattern recognition.

The present invention also provides a foot-worn, in-shoe based sensorsystem configured to measure activity in a wearer of a shoe configuredto be donned on a user's foot. A sensor array is associated with theshoe, including a plurality of force sensitive resistors and a tri-axialaccelerometer. An electronic processor is operably coupled to the sensorarray to receive data from the sensor array and analyzing the data todetermine an activity level of the user based on a determinedinclination of the shoe during stance phase.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention; and, wherein:

FIG. 1 is a schematic view of a shoe with a multi-sensor insole inaccordance with an embodiment of the present invention;

FIG. 2 is a flow chart of a method for determining incline of a foot orshoe, and a method of determining energy expenditure of an individual inaccordance with an embodiment of the present invention;

FIG. 3 a is an exemplary graph of force vs. time for the sum of theforce sensor outputs showing a portion of stance used to determineincline;

FIG. 3 b is an exemplary graph of acceleration vs. time for the vectormagnitude showing a portion of stance used to determine incline; and

FIG. 3 c is an exemplary graph of angle vs. time showing an incline atthe portion of stance used to determine incline in FIGS. 3 a and 3 b.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT(S)

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features illustrated herein, andadditional applications of the principles of the inventions asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the invention.

The embodiments of the present invention described herein provide for aninexpensive, foot-worn monitor that includes incline in activitymeasurement to provide improved assessment of physical activity of thefoot-worn monitor. In one aspect, the foot-worn monitor can include ashoe or pair of shoes with multi-sensor insoles that include forcesensors and accelerometers in order to determine incline and/ororientation of the shoe during gaited motion. The terms “shoe” or“shoes” are used broadly herein to mean any footwear, whethercommercially available or custom made for carrying the sensors, such asshoe, sneaker, boot, sandal, slipper, athletic footwear, sock, etc. Morespecifically, the insole can include a plurality of force sensitiveresistors in the heel and toe of the insole, and a tri-axialaccelerometer in an arch section of the insole. The insole can be formedof a polymeric material such as silicone. In use, an individual can wearthe insole in the shoe, and the orientation with respect to the earth'sgravitational field of the surface traversed by the shoe can bedetermined using the sensors in the insole. The force sensors candetermine when the shoe is flat on the ground and thus also provide thestep count.

As illustrated in FIG. 1, a foot-worn activity monitor, indicatedgenerally at 10, in accordance with the present invention is shown foruse in measuring activity in a wearer of the shoe. The activity monitor10 can include a shoe 20, an insole, indicated generally at 30, a sensorarray, indicated generally at 50, associated with the insole, and anelectronic processor, indicated generally at 70, operably coupled to thesensor array.

The shoe 20 can be an ordinary shoe or boot as known in the art. Forexample, the shoe 20 can be a sneaker or dress shoe that can be donnedon a natural foot or a prosthetic foot of the user. The shoe 20 can bepart of a pair of shoes and both shoes can include the foot wornactivity monitor described herein.

The insole 30 can be sized and shaped to fit within the shoe. The insole30 can be formed of an elastomeric and/or polymeric material such asrubberized silicone. The insole 30 can have a toe section 32, a heelsection 34, and an arch section 36 disposed between the toe section andheel section.

The sensor array 50 can be associated with the insole 30. The sensorarray 50 can measure the incline or orientation of the shoe, and theforce applied to the shoe during motion or activity of the user. In oneaspect, the sensors of the sensor array 50 can be imbedded in theelastomeric and/or polymeric material of the insole 30. The sensor array50 can be attached externally to the shoe, for instance fastened to theshoelaces or attached to another surface of the shoe.

The sensor array 50 can include an accelerometer, a two-axisaccelerometer, a tri-axial accelerometer, a force sensor, a strain gage,a level, a force sensitive resistor, a pressure sensor, a pressuresensing array, and the like. For example, in one aspect, the sensorarray 50 can include one or more force sensitive resistors 52 placedunderneath the toe section 32 of the insole 30, and one or more forcesensitive resistors 54 placed underneath the heel section 34 of theinsole. Additionally, the sensor array can include a tri-axialaccelerometer 56 placed underneath the arch section 36 of the insole. Inthis way, the sensor array 50 can sense the forces applied to the shoe,the step count of the shoe, and the inclination or orientation of theshoe with respect to level or the gravitational field of the earth.

In accordance with one aspect of the invention, the insole 30 can besegmented into a plurality of parts or pieces to fit within differentsize shoes and accommodate different sized feet. For example, the insolecan include the toe piece 32, the heel piece 34, and the middle piece orarch section 36 which can be connected but movable with respect to oneanother. The toe piece can include the one or more force sensitiveresistors 52 and can be positioned at a toe of the shoe. The heel piece34 can include the one or more force sensitive resistors 54 and can bepositioned at a heel of the shoe. The middle piece 36 can include thetri-axial accelerometer 56 and/or circuits.

Additionally, the sensor array can include electronic circuitry incommunication with the sensors 52, 54 and 56 to route the sensor data tothe electronic processor 70. For example, the circuitry can include aprimary circuit board 58 with the tri-axial accelerometer and amultiplexer, and a secondary circuit board 60 operatively coupled to theprimary circuit board with connections for the force sensitiveresistors, a voltage divider coupled to an op-amp buffer, and amultiplexer.

The electronic processor 70 can be operably coupled to the sensor array50 to receive data from the sensors of the sensor array. The electronicprocessor 70 can analyze the data to determine an activity level of theuser. The electronic processor can include a microprocessor, amicrocomputer, a computer, and the like. In this way, the electronicprocessor 70 can analyze data from the force sensors and tri-axialaccelerometer to determine the energy expenditure of an individualwearing the shoe based on the force applied to the shoe and theorientation of the shoe with respect to the ground over a period oftime.

The present invention also provides for a method for analyzing motion,and/or shoe inclination during motion, of an individual, and for methodfor measuring activity in the individual. At least a tri-axialaccelerometer is affixed with respect to a user's foot. The tri-axialaccelerometer can be affixed to a shoe. For example, the accelerometercan be part of an insole disposed in the shoe, such as at an archsection or middle piece of the insole. Alternatively, the accelerometercan be in a separate enclosure that is tied to the shoelaces or affixedexternally to the shoe. Accelerometer data is collected from thetri-axial accelerometer. Incline during stance phase is determined 100(FIG. 2) based on the accelerometer data from the tri-axialaccelerometer using an electronic processor.

Incline can be estimated utilizing the equation (1):

$\begin{matrix}{\theta = {\sin^{- 1}\left( \frac{A_{x} + A_{y}}{\sqrt{2\left( {A_{x}^{2} + A_{y}^{2} + A_{z}^{2}} \right)}} \right)}} & (1)\end{matrix}$where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured bythe tri-axial accelerometer in x, y and z directions, respectively, andθ is the angle of incline.

Offset between the shoe and the sensor board when the system isinitialized and the foot is on level ground can be determined 102 (FIG.2) utilizing the equation (2):

$\begin{matrix}{\theta_{o} = {\sin^{- 1}\left( \frac{A_{x_{o}} + A_{y_{o}}}{\sqrt{2\left( {A_{x_{o}}^{2} + A_{y_{o}}^{2} + A_{z_{o}}^{2}} \right)}} \right)}} & (2)\end{matrix}$where A_(xo), A_(yo) and A_(zo) are magnitudes of acceleration measuredby the tri-axial accelerometer in x, y and z directions, respectively,measured when the foot is initially flat on level ground, and θ_(o) isthe offset angle between the shoe and the sensor board.

Incline during gait can be determined 100 (FIG. 2) utilizing theequation (3):

$\begin{matrix}{\theta = {{\sin^{- 1}\left( \frac{A_{x} + A_{y}}{\sqrt{2\left( {A_{x}^{2} + A_{y}^{2} + A_{z}^{2}} \right)}} \right)} - \theta_{o}}} & (3)\end{matrix}$where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured bythe tri-axial accelerometer in x, y and z directions, respectively,measured when the foot is in stance phase, and θ is the angle ofincline. An example of determining incline is shown in FIG. 3 c. Theangle can be determined during stance phase, examples of which are shownin FIGS. 3 a and 3 b.

Stance phase can be determined 104 (FIG. 2) based on the accelerometerdata from the tri-axial accelerometer using the electronic processor. Amagnitude of acceleration vector can be determined utilizing theequation (4):|{right arrow over (A)}|=√{square root over (A _(x) ² +A _(y) ² +A _(z)²)}  (4)where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured bythe tri-axial accelerometer in x, y and z directions, and A is themagnitude of the acceleration vector. When the foot is flat on thefloor, the magnitude of total acceleration should be substantially equalto 1 g during stance phase. An example of the acceleration data measuredfrom the accelerometer is shown in FIG. 3 b. Also shown is thedetermination of stance phase.

The energy expenditure of the individual can be determined 108 (FIG. 2)based on the accelerometer data from the tri-axial accelerometer usingthe electronic processor.

Alternatively, stance phase can be determined 104 (FIG. 2) utilizing aplurality of force sensitive resistors affixed with respect to theuser's foot. Again, the plurality of force sensitive resistors can beaffixed to a shoe. For example, the force sensitive resistors can bepart of an insole disposed in the shoe, such as at toe and heel piecesof the insole. Force data can be collected from the plurality of forcesensitive resistors. Stance phase can be determined 104 (FIG. 2) basedon the force data from the plurality of force sensitive resistors usingthe electronic processor. An example of the force data measured from theforce sensitive resistors is shown in FIG. 3 a. Also shown is thedetermination of stance phase.

The energy expenditure of the individual can be determined 108 (FIG. 2)based on the force data and the inclination of the shoe with respect tothe ground over a period of time using the electronic processor. Forexample, energy expenditures of activities such as walking and runningcan be quantified based on the individual's speed, and energyexpenditures are known to increase while going uphill and decrease whilegoing downhill. The speed of the individual can be determined from thestep rate multiplied by the step length (or stride rate multiplied bystride length), and then adjusted accordingly if the surface is notlevel. For instance, this could be done using a lookup table (withinterpolation if necessary) using published energy expenditures giventhe incline of the surface, or an appropriate multiplication factorcould be applied to a standard calculation of energy expenditure (e.g.calories burned) on a level surface. In addition, information from forcesensors can be used to further refine the determination of energyexpenditure. Thus, the energy expenditure can be determined based on therate of steps, the step length (or stride rate and stride length), andthe inclination of the shoe with respect to the ground during stancephase over a period of time. Similarly, pattern recognition can be usedto identify specific activities (e.g. swinging on playground swings,hopping on one foot, etc.) to use known energy expenditures.

Affixing the accelerometer and the force sensitive resistors can includepositioning a toe piece of an insole with at least one force sensitiveresistor at a toe of the shoe; positioning a heel piece of the insolewith at least one force sensitive resistor at a heel of the shoe;positioning a middle piece of the insole with the tri-axialaccelerometer in the shoe between the toe and heel pieces; positioningan insole with at least one force sensitive resistor and theaccelerometer outside of the shoe.

A method for making a shoe that measures the activity level of thewearer of the shoe includes preparing a mold of an insole of the shoe.An insole can be formed by adding an uncured polymeric material to themold and allowing it to cure. A plurality of force sensitive resistorscan be placed in the toe and heel of the mold or insole. A tri-axialaccelerometer can be placed in the arch section of the mold or insole.The plurality of force sensitive resistors and the tri-axialaccelerometer can be coupled to an electronic processor to determine theenergy expenditure of an individual wearing the shoe based on the forceapplied to the shoe and the inclination of the shoe with respect to theground over a period of time. The cured insole along with the sensorscan be placed into the shoe.

The tri-axial accelerometer can be enclosed within a small housing withthe electronic processor, and can be affixed externally to the shoe. Itcan be tied to the laces of the shoe, or clipped to the heel of theshoe, or another surface of the shoe.

It is to be understood that the above-referenced arrangements are onlyillustrative of the application for the principles of the presentinvention. Numerous modifications and alternative arrangements can bedevised without departing from the spirit and scope of the presentinvention. While the present invention has been shown in the drawingsand fully described above with particularity and detail in connectionwith what is presently deemed to be the most practical and preferredembodiment(s) of the invention, it will be apparent to those of ordinaryskill in the art that numerous modifications can be made withoutdeparting from the principles and concepts of the invention as set forthherein.

1. A method for analyzing motion of an individual, comprising: a) affixing at least a tri-axial accelerometer with respect to a user's foot; b) collecting accelerometer data from the tri-axial accelerometer; c) determining incline during stance phase based on the accelerometer data from the tri-axial accelerometer using an electronic processor; d) determining stance phase based on the accelerometer data from tri-axial accelerometer using the electronic processor; and e) determining an energy expenditure of the individual based on the inclination of the shoe with respect to the ground over a period of time using the electronic processor.
 2. A method in accordance with claim 1, further comprising: determining energy expenditure of the individual based on the accelerometer data from the tri-axial accelerometer using the electronic processor.
 3. A method in accordance with claim 1, further comprising: affixing a plurality of force sensitive resistors with respect to the user's foot; collecting force data from the plurality of force sensitive resistors; and determining stance phase based on the force data from the plurality of force sensitive resistors using the electronic processor.
 4. A method in accordance with claim 3, further comprising: determining an energy expenditure of the individual based on the force applied to the shoe and the inclination of the shoe with respect to the ground over a period of time using the electronic processor.
 5. A method in accordance with claim 1, wherein determining stance phase further includes determining a magnitude of acceleration vector utilizing the equation: |{right arrow over (A)}|=√{square root over (A _(x) ² +A _(y) ² +A _(z) ²)} where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured by the tri-axial accelerometer in x, y and z directions, and A is the magnitude of the acceleration vector; and wherein the magnitude of total acceleration being substantially equal to 1 g during stance phase.
 6. A method in accordance with claim 1, further comprising: estimating incline utilizing the equation: $\theta = {\sin^{- 1}\left( \frac{A_{x} + A_{y}}{\sqrt{2\left( {A_{x}^{2} + A_{y}^{2} + A_{z}^{2}} \right)}} \right)}$ where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured by the tri-axial accelerometer in x, y and z directions, respectively, and θ is the angle on incline.
 7. A method in accordance with claim 1, further comprising: determining offset between the shoe and the sensor board when the system is initialized and the foot is on level ground utilizing the equation: $\theta_{o} = {\sin^{- 1}\left( \frac{A_{x_{o}} + A_{y_{o}}}{\sqrt{2\left( {A_{x_{o}}^{2} + A_{y_{o}}^{2} + A_{z_{o}}^{2}} \right)}} \right)}$ where A_(xo), A_(yo) and A_(zo) are magnitudes of acceleration measured by the tri-axial accelerometer in x, y and z directions, respectively, measured when the foot is initially flat on level ground, and θ_(o) is the offset angle between the shoe and the sensor board; and determining incline during gait utilizing the equation: $\theta = {{\sin^{- 1}\left( \frac{A_{x} + A_{y}}{\sqrt{2\left( {A_{x}^{2} + A_{y}^{2} + A_{z}^{2}} \right)}} \right)} - \theta_{o}}$ where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured by the tri-axial accelerometer in x, y and z directions, respectively, measured when the foot is in stance phase, and θ is the angle of incline.
 8. A method in accordance with claim 1, further comprising: positioning a toe piece of an insole with at least one force sensitive resistor at a toe of the shoe; positioning a heel piece of the insole with at least one force sensitive resistor at a heel of the shoe; and positioning a middle piece of the insole with the tri-axial accelerometer in the shoe between the toe and heel pieces.
 9. A method for measuring activity in an individual, comprising: a) collecting data from a multi-sensor insole disposed in a shoe, including force data from a plurality of force sensitive resistors and accelerometer data from a tri-axial accelerometer; b) analyzing the data from the sensors of the multi-sensor insole with an electronic processor to determine the energy expenditure of the individual based on the force data and inclination of the shoe with respect to the ground during stance phase over a period of time; and c) determining stance phase based on the force data from the plurality of force sensitive resistors using the electronic processor.
 10. A method in accordance with claim 9, further comprising: estimating the inclination utilizing the equation: $\theta = {\sin^{- 1}\left( \frac{A_{x} + A_{y}}{\sqrt{2\left( {A_{x}^{2} + A_{y}^{2} + A_{z}^{2}} \right)}} \right)}$ where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured by the tri-axial accelerometer in x, y and z directions, respectively, and θ is the angle of inclination.
 11. A method in accordance with claim 9, further comprising: determining offset between the shoe and the sensor board when the system is initialized and the foot is on level ground utilizing the equation: $\theta_{o} = {\sin^{- 1}\left( \frac{A_{x_{o}} + A_{y_{o}}}{\sqrt{2\left( {A_{x_{o}}^{2} + A_{y_{o}}^{2} + A_{z_{o}}^{2}} \right)}} \right)}$ where A_(xo), A_(yo) and A_(zo) are magnitudes of acceleration measured by the tri-axial accelerometer in x, y and z directions, respectively, measured when the foot is initially flat on level ground, and θ_(o) is the offset angle between the shoe and the sensor board; and determining incline during gait utilizing the equation: $\theta = {{\sin^{- 1}\left( \frac{A_{x} + A_{y}}{\sqrt{2\left( {A_{x}^{2} + A_{y}^{2} + A_{z}^{2}} \right)}} \right)} - \theta_{o}}$ where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured by the tri-axial accelerometer in x, y and z directions, respectively, measured when the foot is in stance phase, and θ is the angle of incline.
 12. A method in accordance with claim 9, further comprising: determining stance phase based on the force data and the accelerometer data and utilizing the equations: |{right arrow over (A)}|=√{square root over (A _(x) ² +A _(y) ² +A _(z) ²)} where A_(x), A_(y) and A_(z) are magnitudes of acceleration measured by the tri-axial accelerometer in x, y and z directions, and A is the magnitude of the acceleration vector; and wherein the magnitude of total acceleration being substantially equal to 1 g during stance phase.
 13. A method in accordance with claim 12, further comprising: positioning a toe piece of an insole with at least one force sensitive resistor at a toe of the shoe; positioning a heel piece of the insole with at least one force sensitive resistor at a heel of the shoe; and positioning a middle piece of the insole with the tri-axial accelerometer in the shoe between the toe and heel pieces. 